Preparation of alkylene carbonates

ABSTRACT

Alkylene carbonates, particularly ethylene carbonate, are prepared by the reaction of an alkylene oxide with carbon dioxide in the presence of a catalyst at temperatures in the region of the critical temperature of carbon dioxide, preferably 25°-70° C. and at autogenerated pressures, typically 30 to 200 kg/cm 2  gauge. The conversion of alkylene oxide to alkylene carbonate can be carried out in the presence of water while minimizing the undesirable hydrolysis of the carbonate to athe corresponding alkylene glycol. With certain catalysts the presence of water improves the selectivity to the formation of the carbonate.

This Application is a division of Ser. No. 502,024 filed June 7, 1983,now U.S. Pat. No. 4,841,072 which was a continuation of Ser. No. 326,447filed Dec. 2, 1981, now abandoned.

PRIOR ART

The invention relates to a process for the preparation of alkylenecarbonates by the reaction of the corresponding alkylene oxide withcarbon dioxide. Such reactions are well known in the art. Alkylenecarbonates are useful as solvents or as a source of the correspondingglycols. They are of particular interest as intermediates in the processof converting ethylene oxide into ethylene glycol while avoiding theinefficiency associated with the conventional hydration process.

Several processes have been disclosed for a single step hydration ofalkylene oxides to glycols in the presence of a catalyst and carbondioxide. Such processes are said to make possible the reduction in theamount of water used. The removal of excess water is a major expense inthe conventional hydration process. The carbon dioxide is not consumedin the process, but it has been suggested that the hydration proceedsvia the alkylene carbonate as an intermediate compound.

U.S. Pat. No. 3,922,314 discloses a process for the hydration ofethylene oxide to ethylene glycol which uses no catalyst, but operateswith an aqueous ethylene oxide solution containing at least 8 wt %ethylene oxide and at least 0.1 wt % carbon dioxide.

A catalytic process is described in British patent 1,177,877 (or U.S.Pat. No. 3,629,343). Alkylene oxides are hydrated to the glycols attemperatures of 80°-220° C. and pressures of 10-180 atmospheres in thepresence of a halide catalyst. Preferred are alkali metal or quaternaryammonium halides, particularly bromides and iodides. Alkali metalhydroxides, carbonates, or bicarbonates were said to be beneficial.

A similar process is discussed in U.S. Pat. No. 4,160,116 wherequaternary phosphonium halides, preferably the iodides and bromides wereused to catalyze the hydration of alkylene oxides in the presence ofcarbon dioxide. The temperature is 50°-200° C. and the pressure 3-50kg/cm².

Still another such process is disclosed in published Japanese patentapplication 81-45426, in which molybdenum and/or tungsten compounds arecombined with known catalysts such as alkali metal halides, quaternaryammonium or phosphonium salts, organic halides, and organic amines. Thereaction is stated to be carried out at 20°-250° C. and 0-30 kg/cm²gauge.

The formation of alkylene carbonates, as opposed to the hydration ofalkylene oxides to glycols, takes place in the prior art to be discussedwith no water present. Catalysts and reaction conditions similar tothose described above for the hydration of alkylene oxides have beendisclosed to be useful.

In U.S. Pat. No. 2,667,497 magnesium or calcium halides were used at150°-250° C. and 500-2000 psi to produce alkylene carbonates from thecorresponding oxides.

U.S. Pat. No. 2,766,258 discloses the use of quaternary ammoniumhydroxides, carbonates, and bicarbonates to catalyze the reaction ofalkylene oxides with carbon dioxide. The reaction was carried out attemperatures between 100°-225° C. and pressures of 300-500 psig.

The quaternary ammonium halides were used by the patentees in U.S. Pat.No.2,773,070 at temperatures of 100°-225° C. and pressures greater than800 psi.

Amines were the catalyst used for the reaction by the patentees in U.S.Pat. No. 2,773,881. The reaction was carried out at 100°-400° C. andmore than 500 psi.

Three patents issued to the same assignee, i.e. U.S. Pat. Nos.2,994,705; 2,994,704; and 2,993,908 disclose substantially the sameconditions, 93°-260° C. and 8-212 kg/cm² gauge, with organic phosphoniumhalides, organic sulfonium halides, and urea hydrohalides given ascatalysts for the preparation of alkylene carbonates from thecorresponding oxirane compound.

Hydrazine or a halide salt thereof was used to catalyze the reaction bythe patentees in U.S. Pat. No. 3,535,341 at temperatures of 100°-250° C.An anion exchange resin containing quaternary ammonium groups wasdisclosed in U.S. Pat. No. 4,233,221 as useful for vapor-phase reaction.

Organic antimony halides were shown in published Japanese patentapplication 80-122,776 to make possible the formation of alkylenecarbonates, at room temperature to 120° C., in a water-free mixture. Thetime required in the single example carried out at room temperature wasabout 5 days, a generally impractical period of time.

I have now discovered that the reaction of alkylene oxides to thecorresponding carbonates can be carried out with known catalysts atlower temperatures than heretofore used in the art. Further, thereaction is operable even in the presence of substantial amounts ofwater. The hydrolysis of the carbonates to glycols can be minimized andthe principal product is the carbonate, as will be seen in the followingdiscussion.

SUMMARY OF THE DISCLOSURE

Alkylene oxides may be reacted with carbon dioxide to form alkylenecarbonates in the presence of a catalytic amount of suitable catalystsat relatively low temperatures in the range of about 20°-90° C. and inthe presence of water. Preferably the temperature will be about 30°-70°C. The pressure at which the reaction is carried out is in the range ofabout 25-200 kg/cm² gauge, and may be autogenerated. The mol ratio ofcarbon dioxide to alkylene oxide is in the range of 1/1-100/1 andpreferably about 2/1-10/1. Suitable catalysts include a member ormembers of the group consisting of quaternary organic ammonium andphosphonium halides, organic sulfonium halides, and organic antimonyhalides, particularly methyl triphenyl phosphonium iodide, tetra-ethylammonium bromide, and tetraphenyl antimony bromide. The correspondingcarboxylates may also be used. The quantity of catalyst used isgenerally within the range of 0.01 to 0.15 mols per mol of alkyleneoxide, preferably 0.02 to 0.10.

Contrary to previous expectations, water may be present in substantialamounts, even exceeding those used in prior art hydration processes, butwithout formation of significant amounts of glycol. Useful mol ratios ofwater to alkylene oxide are 0.1/1-20/1. With certain catalysts, theeffect of water actually is to improve the selectivity of the conversionof the oxirane to the carbonate.

In another embodiment, the invention comprises a process for reactingalkylene oxides with carbon dioxide to form alkylene carbonates atrelatively low temperatures in the range of about 20°-90° C. in thepresence of at least one catalyst selected from the group consisting ofquarternary organic ammonium and phosphonium halides and carboxylatesand organic sulfonium halides and carboxylates. Such catalysts havehitherto been employed at operating temperatures higher than those nowfound to be useable.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Heretofore, those familiar with the reaction of alkylene oxides withcarbon dioxide to form alkylene carbonates have carried out the reactionat temperatures generally in the range of 100°-300° C., particularlyabout 150°-225° C. Although it was not generally discussed in detail, itwill be seen from prior art disclosures that the reaction was carriedout in the practical absence of water. For Example, in U.S. Pat. No.4,233,221 the reactants were dried by condensation of water aftercompression so that the moisture level of the reactant gases was quitelow, estimated to be about 0.2 mol percent. Since the hydrolysis ofcarbonates was known to take place at elevated temperatures and withcatalysts also useful for the direct hydrolysis of alkylene oxides toglycols, it seems probable that prior workers in the art avoided waterif only the carbonate was to be produced. Otherwise, hydrolysis to theglycol could be expected.

Surprisingly, I have found that when the reaction of alkylene oxideswith carbon dioxide is undertaken at temperatures substantially lowerthan taught by the prior art, that the presence of water can be not onlytolerated, but actually may be beneficial in some instances. Alkylenecarbonates can be prepared with minimal losses by hydrolysis to theglycols. This process is particularly useful when applied to a streamcombining carbon dioxide, ethylene oxide, and water obtained byextraction of ethylene oxide from a dilute aqueous solution withnear-critical or supercritical carbon dioxide.

The reaction may be carried out at temperatures in the range of about20°-90° C., preferably 25°-80° C., especially 30°-70° C. Althoughlowering the temperature would be expected to increase the reactiontime, nevertheless reasonable periods in the general range of 2-8 hoursmay be achieved by properly selecting the amount and type of catalystand the other reaction conditions. In one embodiment, the temperatureused is established by the ambient conditions available for cooling thefeed mixture and thus would be in the range of about 20°-30° C.

Pressure is not an especially critical variable in the reaction.Typically, it will be in the range of about 25-200 kg/cm² gauge and ifthe temperature is sufficiently low, will be autogenerated and thusestablished by the feed composition and the temperature at which thereaction is carried out.

The molar ratio of carbon dioxide to alkylene carbonate may range from1/1 to 100/1. Usually a ratio greater than 1/1 would be selected,preferably 2/1 to 10/1. Where the process of the invention is associatedwith the extraction of alkylene oxide by (near) super-critical carbondioxide the ratio may be 40/1-60/1, with satisfactory results obtained.

It is of particular importance that water does not appear to hydrolyzealkylene carbonates to the glycols to a significant extent underconditions found suitable for the process of the invention. At highertemperatures, the amount of glycols produced would be expected toincrease until eventually the process would no longer producecarbonates, but glycols, instead as disclosed in the patents mentionedearlier. No limit has been established on the amount of water which canbe tolerated, in fact, amounts well in excess of those useful for thedirect hydration of alkylene oxides to glycols have been demonstrated,as will be seen in subsequent examples. Remarkably, it has beendiscovered that the presence of water may have a beneficial effect onthe selectivity of the reaction to produce carbonate, contrary to whatmight be expected. This effect may be more pronounced in associationwith certain catalysts, particularly those in which the bond between thehalide atom and the rest of the molecule is ionic, rather than covalentin nature.

The catalysts found useful in the process of the invention include manyof those known in the art, but used now under significantly alteredconditions. Broad classes of compounds which may be useful include oneor more members of the group consisting of organic quaternary ammoniumor phosphonium halides organic sulfonium halides, and organic antimonyhalides. The corresponding carboxylates also may be used. Examples ofcompounds which may be employed are the following ammonium compoundstetraethyl ammonium bromide, and tetra ethyl ammonium iodide. Specificphosphonium compounds include methyl triphenyl phosphonium iodide andmethyl triphenyl phosphonium bromide. Sulfonium compounds may includetrimethyl sulfonium iodide and trimethyl sulfonium bromide. Antimonycompounds have been found quite effective when no water is present, butappear to be adversely affected when water is included. Typicalcompounds are tetraphenyl antimony bromide and triphenyl antimonydichloride. Particularly preferred catalysts when water is present aremethyl triphenyl phosphonium iodide and tetraethyl ammonium bromide. Ofthe halides, bromides and iodides are preferred.

The amount of catalyst will be similar to that used in other processes,about 0.01-0.15 mols of the catalyst per mol of alkylene oxide may beused, preferably 0.02-0.1 mols per mol, although larger or smalleramounts are not intended to be excluded.

While other workers in the field have indicated that relatively hightemperatures of 100° C. or preferably more would be used either to formalkylene carbonates when no water was present, or alkylene glycols whenwater was available to hydrolyze alkylene oxides, it has been found thatby carrying out the reaction at low temperatures in the range of about20°-90° C., preferably 30°-70° C., one can produce alkylene carbonatesand even in the presence of water.

The reaction to form carbonates may be carried out in the presence ofsubstantial amounts of water. At higher temperatures typical of theprior art, glycols would be expected when water is present and, in fact,this is the basis for several processes as previously discussed. As willbe seen, by operating at relatively low temperatures, it is possible tominimize hydrolysis and to form carbonates instead.

EXAMPLE 1

A sample of the catalyst being tested is introduced to a 130 cc bombproduced by the Parr Instrument Company. Samples of ethylene oxide andcarbon dioxide are charged at -78° C. by immersing the bomb in adry-ice/ acetone bath. The bomb is then closed and placed in a 36° C.bath so that the internal temperature of the bomb is increased to 30° C.and the reaction proceeds. Agitation is via a magnetically driven disk.After a suitable period of time, the bomb is removed from the bath andthe contents analyzed. The results of a number of such tests are shownin Table A below.

                                      TABLE A                                     __________________________________________________________________________    Test                                                                             Feed, millimols                                                                       Catalyst,                                                                          Bath                                                                             Time,                                                                             Max. Pressure                                                                         EO*  EC**                                      No.                                                                              EO* CO.sub.2                                                                          gms***                                                                             °C.                                                                       hrs kg/cm.sup.2 gauge                                                                     Conv. %                                                                            Sel. %                                    __________________________________________________________________________    1  13.6                                                                              681 a 0.1456                                                                           36 19.5                                                                              28.1    51.7 --                                        2  13.6                                                                              681 b 0.4385                                                                           36 19.5                                                                              29.5    55   16                                        3  18.2                                                                              681 c 0.3654                                                                           32 19.5                                                                              18.3    94   88.2                                      4  15.9                                                                              681 d 0.3064                                                                           37 18.5                                                                              15.5    37.7 --                                        5  18.2                                                                              1022                                                                              e 0.3881                                                                           38 19.5                                                                              30.6    51.1 --                                        6  22.7                                                                              1022                                                                              f 0.2406                                                                           38 19.5                                                                              78.1    77.9 50.4                                      __________________________________________________________________________     *EO = ethylene oxide                                                          **EC = ethylene carbonate                                                     ***a = trimethyl sulfonium iodide                                             b = methyl triphenyl phosphonium iodide                                       c = tetraphenyl antimony bromide                                              d = triphenyl antimony dichloride                                             e = methyl triphenyl phosphonium bromide                                      f = tetraethyl ammonium bromide                                          

It has been discovered that water may be present without formation ofsignificant amounts of glycols, provided that the temperature issufficiently low. Surprisingly, it has been found that water has abeneficial effect on the selectivity to the carbonate with somecatalysts, while with others the selectivity appears to be suppressed.

EXAMPLE 2 Effect of Water on Catalysts

The procedure of Example 1 is followed except that varying amounts ofwater are introduced to the Parr bomb, with the following results.

                                      TABLE B                                     __________________________________________________________________________    Test                                                                             Feed, millimols                                                                         Catalyst,                                                                          Bath                                                                             Time,                                                                             Max. Pres.                                                                            EO   EC                                      No.                                                                              EO  CO2                                                                              H2O                                                                              gms* °C.                                                                       hrs kg/cm2 gauge                                                                          Conv. %                                                                            Sel. %                                  __________________________________________________________________________     7 19.3                                                                              1022                                                                             -- c 0.5507                                                                           33 19.5                                                                              27.8    91.1 88.5                                     8 18.2                                                                              1022                                                                             10 c 0.5466                                                                           34 19.5                                                                              27.4    95.6 47.1                                     9 20.4                                                                              1022                                                                              5 b 0.4380                                                                           37 21  44.3    86   35                                      10 20.4                                                                              1022                                                                             20 b 0.4227                                                                           37 21  42.5    92   47.4                                    11 20.4                                                                              1022                                                                             40 b 0.4319                                                                           37 21  43.2    93   63                                      12 22.7                                                                              1022                                                                             80 b 0.4365                                                                           37 21  41.1    83.8 76                                      __________________________________________________________________________     *c = tetraphenyl antimony bromide                                             b = methyl triphenyl phosphonium iodide                                  

The data of Table B show that the presence of water appears to have norecognizable effect on the overall conversion of ethylene oxide, theselectivity to ethylene carbonate is reduced when catalyst "c" is used,while when catalyst "b" is employed the selectivity to ethylenecarbonate is surprisingly improved. Catalyst "c" would be more suitablefor a reaction system in which the amount of water present is not large.Note that the ratio of water to ethylene oxide is about 0.55/1 comparedto the theoretical ratio of 1/1 for the hydrolysis reaction. Catalyst"b" appears less effective when no water is present (see test 2) but itsperformance is enchanced when water is used. Note that the ratios forthis catalyst shown reach nearly 4/1 water/EO.

Although the process of the invention is particularly useful inconnection with the formation of ethylene carbonate, it is more widelyapplicable to other oxirane compounds, as will be seen in the followingexample.

EXAMPLE 3

A sample of the catalyst being tested and water (if used) is introducedto a 130 cc Parr bomb. Samples of propylene oxide and carbon dioxide arecharged at -78° C. by immersing the bomb in a dry-ice/acetone bath. Thebomb is then closed and placed in a 36° C. bath so that the internaltemperature of the bomb is increased to 30° C. and the reactionproceeds. After a suitable period of time, the bomb is removed from thebath and the contents analyzed. The results of a number of such testsare shown in Table C below.

                                      TABLE C                                     __________________________________________________________________________    Test                                                                             Feed, millimols                                                                         Catalyst,                                                                          Bath                                                                             Time,                                                                             Max. Pres.                                                                            PO   PC**                                    No.                                                                              PO* CO2                                                                              H2O                                                                              gms***                                                                             °C.                                                                       hrs kg/cm2 gauge                                                                          Conv. %                                                                            Sel. %                                  __________________________________________________________________________    13 20.3                                                                              1022                                                                             -- a 0.5511                                                                           35 21  42.6    96.2 90.3                                    14 20.6                                                                              1022                                                                             -- b 0.4385                                                                           36 21  34.2    60.2 25.4                                    15 20.2                                                                              1022                                                                             -- c 0.2401                                                                           36 21  56.1    85.0 58.3                                    16 20.4                                                                              1022                                                                              5 b 0.4382                                                                           36 21  47.3    88.2 34.6                                    17 20.6                                                                              1022                                                                             20 b 0.4378                                                                           36 21  52.8    89.7 56.4                                    18 20.1                                                                              1022                                                                             40 b 0.4386                                                                           36 21  54.2    87.4 68.3                                    19 20.4                                                                              1022                                                                             80 b 0.4391                                                                           36 21  62.1    91.4 82.3                                    __________________________________________________________________________     *PO = propylene oxide                                                         **PC = propylene carbonate                                                    ***a = tetraphenyl antimony bromide                                           b = methyl triphenyl phosphonium iodide                                       c = tetraethyl ammonium bromide                                          

EXAMPLE 4

The experimental procedure of Example 3 was followed with 1,2-butyleneoxide charged in lieu of propylene oxide. The results of a number ofsuch tests are shown in Table D below.

                                      TABLE D                                     __________________________________________________________________________    Test                                                                             Feed, millimols                                                                         Catalyst,                                                                          Bath                                                                             Time,                                                                             Max. Pres.                                                                            BO   BC**                                    No.                                                                              BO* CO2                                                                              H2O                                                                              gms***                                                                             °C.                                                                       hrs kg/cm2 gauge                                                                          Conv. %                                                                            Sel. %                                  __________________________________________________________________________    20 20.4                                                                              1022                                                                             -- a 0.5513                                                                           36 21  44.8    92.1 87.6                                    21 20.7                                                                              1022                                                                             -- b 0.4378                                                                           36 21  47.2    58.3 22.6                                    22 20.1                                                                              1022                                                                             -- d 0.2436                                                                           36 21  42.6    82.0 53.2                                    23 20.1                                                                              1022                                                                              5 b 0.4386                                                                           36 21  51.8    89.2 40.5                                    24 20.8                                                                              1022                                                                             20 b 0.4392                                                                           36 21  43.8    91.4 59.8                                    25 20.2                                                                              1022                                                                             40 b 0.4369                                                                           36 21  56.2    93.4 72.8                                    26 20.6                                                                              1022                                                                             80 b 0.4381                                                                           36 21  53.6    90.8 84.3                                    __________________________________________________________________________     *BO = 1,2butylene oxide                                                       **BC = 1,2butylene carbonate                                                  ***a = tetraphenyl antimony bromide                                           b = methyl triphenyl phosphonium iodide                                       c = tetraethyl ammonium bromide                                          

EXAMPLE 5

A sample of the catalyst being tested, along with H₂ O and solvents(when used) is introduced to a 300 cc electrically heated stainlesssteel autoclave equipped with impeller agitation produced by AutoclaveEngineers, Inc. Samples of ethylene oxide and carbon dioxide are chargedat -78° C. while the autoclave is immersed in a dry-ice/acetone bath.The autoclave is then closed and heated to the desired reactiontemperature. After a suitable period of time, the autoclave is cooledand the contents analyzed. The results of a number of such tests areshown in Table E below.

                                      TABLE E                                     __________________________________________________________________________    Test                                                                             Feed, millimols                                                                             Catalyst,                                                                          Bath                                                                             Time,                                                                             Max. Pres.                                                                            EO   EC****                              No.                                                                              EO* CO.sub.2                                                                         H.sub.2 O                                                                        THF**                                                                             gms***                                                                             °C.                                                                       hrs kg/cm.sup.2 gauge                                                                     Conv. %                                                                            Sel. %                              __________________________________________________________________________    27 347 1590                                                                             346                                                                              1262                                                                              a 20.0                                                                             60 4   52.0    95.6 97.0                                28 695 2794                                                                             695                                                                              --  a 20.0                                                                             60 6   104.8   95.8 90.5                                29 1157                                                                              2113                                                                             583                                                                              --  a 20.0                                                                             50 6   57.7    98.2 95.5                                30 349 1590                                                                             350                                                                              1263                                                                              a 20.0                                                                             70 2   57.3    99.5 96.0                                __________________________________________________________________________     *EO = ethylene oxide                                                          **THF = tetrahydrofuran                                                       ***a = methyl triphenyl phosphonium iodide                                    ****EC = ethylene carbonate                                              

What is claimed:
 1. A process for preparing alkylene carbonates by thereaction of an alkylene oxide with carbon dioxide in the presence of atleast one catalyst selected from the group consisting of organicquaternary ammonium halides, and organic sulfonium halides, at atemperature in the range of 20°-90° C.
 2. The process of claim 1 whereinthe temperature is in the range of 30°-70° C.
 3. The process of claim 1wherein the pressure is in the range of about 25-200 kg/cm² gauge. 4.The process of claim 1 wherein said catalyst is trimethyl sulfoniumiodide.
 5. The process of claim 1 wherein said catalyst is tetraethylammonium bromide.
 6. The process of claim 1 wherein said catalyst ispresent in a ratio of 0.01 to 0.15 ml per mol of alkylene oxide.
 7. Theprocess of claim 1 wherein the mol ratio of carbon dioxide to alkyleneoxide is in the range of about 1/1 to 100/1.
 8. The process of claim 6wherein said mol ratio is about 2/1 to 10/1.
 9. The process of claim 1wherein said alkylene oxide is ethylene oxide.